1. Field of the Invention
The present invention relates to a thermal transfer printing method which uses a printing means such as a thermal head, an optical head or an electrical resistance head, an apparatus, and an intermediate sheet for thermal transfer printing. In particular, the present invention relates to a printing method having good performances in a sublimation type thermal transfer printing on a sheet of plain paper, an apparatus therefor, and an intermediate sheet for thermal transfer printing.
2. Description of the Related Art
In thermal transfer printing, an image is formed on an image receptor by laminating a transfer sheet having a coloring layer on the image receptor and transferring a color image from the transfer sheet directly onto the image receptor using a printing head. There is a method known for forming an image on the image receptor by forming an image on a separate intermediate sheet and then transferring the image from the intermediate sheet to the image receptor (see, for example, Japanese Patent Kokai Publication No. 222877/1983 and U.S. Pat. No. 4,923,848).
Among the thermal transfer printing methods using an intermediate sheet, the sublimation type thermal transfer printing requires an intermediate sheet having thereon a dyeing layer on which a dye is dyed or color developed. An image is formed on the image receptor by forming an image in the dyeing layer of the intermediate sheet and then transferring the dyeing layer carrying the formed image onto the image receptor.
The conventional image, which is formed by transferring the dyeing layer from the intermediate sheet to a sheet of plain paper, is high gloss, so that the formed image has an appearance and a hand feel like an image receptor which is formed by coating the dyeing layer on the sheet of plain paper. Therefore, the formed image has poor configurations as an image on the sheet of plain paper.
The dyeing layer on the intermediate sheet should be maintained on the intermediate sheet when the image is formed on the dyeing layer, while it should be removed from the intermediate sheet when it is transferred to the image receptor. However, no printing method has been developed which satisfies both properties and stably prints the image at a high speed.
When the intermediate sheet sheet is continuous, and a first part of the dyeing layer carrying the image of the intermediate sheet is transferred to the image receptor at the same time as another image is formed on a second part of the dyeing layer of the intermediate sheet, the first and second parts of the dyeing layer of the intermediate sheet should be simultaneously pressed by the head or other means. In addition, when all the colors are printed using a single head, the specific part of the intermediate sheet should be returned to the position of the head. In either case, to carry out the image forming and the image transfer simultaneously, the position of intermediate sheet should be controlled. Consequently, after the image is transferred, the next image forming should be done, which prolongs the total printing time.
When plural cut intermediate sheets are stacked in a sheet feeder, and a thin polymer film is used as a base material of the intermediate sheet, they tend to be wrinkled or to stick to each other in the sheet feeder, since the polymer film has less rigidity than paper. Accordingly, handling of the intermediate sheets is difficult when the plural cut intermediate sheets are stacked in the sheet feeder.
Further, a thermal transfer printing method and apparatus having a simple structure has been desired.